About Growth Charts

Look at any class picture, and you'll see kids of the same age in all shapes and sizes. Some kids look tiny next to their peers, while others literally stand head and shoulders above their classmates.

As easy as it is to make these comparisons and to draw conclusions about what you see, the reality is that kids grow at their own pace. Big, small, tall, short — there is a wide range of healthy shapes and sizes among children.

Genetics, gender, nutrition, physical activity, health problems, environment, hormones, and lifestyle factors like nutrition and physical activity all influence a child's height and weight. And many of these factors can vary widely from family to family.

So how does a doctor figure out whether a child's height and weight measurements are "normal"? Whether he or she is developing on track? Whether any health problems are affecting growth?

A doctor uses growth charts to help answer those questions. Here are some facts about growth charts and what they say about a child's health.

Why Do Doctors Use Growth Charts?

Growth charts are a standard part of any checkup, and they show health care providers how kids are growing compared with other kids of the same age and gender. They also allow doctors and nurses to see the pattern of kids' height and weight gain over time, and whether they're developing proportionately.

Let's say a child was growing along the same pattern until he was 2 years old, then suddenly started growing at a much slower rate than other kids. That might indicate a health problem. Doctors could see that by looking at a growth chart.

Does a Different Pattern Indicate a Problem?

Not necessarily. The doctor will interpret the growth charts in the context of the child's overall well-being, environment, and genetic background. Is the child meeting other developmental milestones? Are there other signs that a child is not healthy? How tall or heavy are the child's parents and siblings? Was the child born prematurely? Has the child started puberty earlier or later than average? These are all factors that the doctor will use to help understand the numbers on the growth chart.

Are All Kids Measured on One Growth Chart?

No. Girls and boys are measured on different growth charts because they grow in different patterns and at different rates.

And one set of charts is used for babies, from birth to 36 months. Another set of charts is used for kids ages 2 to 20 years old. Also, special growth charts are used for children with certain conditions, such as Down syndrome.

What Measurements Are Put on the Charts?

Up until the time babies are 36 months old, doctors measure weight, length, and head circumference.

With older kids, doctors measure weight, height, and body mass index (BMI). It's important to look at and compare weight and height measurements to get a full picture of a child's growth.

Why Is Head Circumference Measured?

In babies, head circumference (the distance around the largest part of the head) can provide clues about brain development. If a baby's head is bigger or smaller than most other kids' or the head circumference stops increasing or increases quickly, it may indicate a problem.

For example, an unusually large head may be a sign of hydrocephalus, a buildup of fluid inside the brain. A head that's smaller than average may be a sign that the brain is not developing properly or has stopped growing.

What Are Percentiles?

Percentiles are measurements that show where a child is compared with others. On the growth charts, the percentiles are shown as lines drawn in curved patterns.

When doctors plot a child's weight and height on the chart, they see which percentile line those measurements land on. The higher the percentile number, the bigger a child is compared with other kids of the same age and gender, whether it's for height or weight; the lower the percentile number, the smaller the child is. For example, if a 4-year-old boy's weight is in the 10th percentile, that means that 10% of boys that age weigh less than he does and 90% of 4-year-old boys weigh more.

How Are Percentiles Determined?

The Centers for Disease Control and Prevention (CDC) created the growth charts that are most commonly used in the United States. They were last updated in 2000. After collecting growth measurements from thousands of U.S. children over a period of time, the CDC was able to show the range of these measurements on one chart, using percentile curves.

Being in a high or a low percentile does not necessarily mean that a child is healthier or has a growth or weight problem. Let's say that 4-year-old boy, who is in the 10th percentile for weight, is also in the 10th percentile for height. So 10% of kids are shorter and weigh less than he does, and most kids — 90% — are taller and weigh more. That just means that he's smaller than average, which usually doesn't mean there is a problem. If his parents and siblings are also smaller than average, and there are other signs that he's healthy and developing well, doctors would likely conclude that there's no cause for concern.

What's the Ideal Percentile for My Child?

There is no one ideal number. Healthy children come in all shapes and sizes, and a baby who is in the 5th percentile can be just as healthy as a baby who is in the 95th percentile.

Ideally, each child will follow along the same growth pattern over time, growing in height and gaining weight at the same rate, with the height and weight in proportion to one another. This means that usually a child stays on a certain percentile line on the growth curve. So if our 4-year-old boy on the 10th percentile line has always been on that line, he is continuing to grow along his pattern, which is a good sign.

What Could Signal a Problem?

A few different growth chart patterns might signal a health problem, such as:

When a child's weight or height percentile changes from a certain pattern it's been following. For example: If height and weight consistently are on the 60th percentile line until a child is 5 years old, then the height has dropped to the 30th percentile at age 6, that might indicate that there's a growth problem because the child is not following his or her previous growth pattern. Many kids may show changes in growth percentiles at certain points in development, when it's normal for growth rates to vary more from child to child. This is particularly common during infancy and puberty.

When kids don't get taller at the same rate at which they're gaining weight. Let's say a boy's height is in the 40th percentile and his weight is in the 85th percentile. (So he's taller than 40% of kids his age, but weighs more than 85% of kids his age.) That might be a problem. On the other hand, if he's in the 85th percentile for height and weight and follows that pattern consistently over time, that usually means that he's a normal child who's just larger than average.

If you have any questions about your child's growth — or growth charts — talk with your doctor.